Heat exchanger



Nov. 19, 1957 R. L. LINCOLN HEAT EXCHANGER INVENTOR..

2 Sheets-Sheet l Filed June 23, 1954 Nov. 19, 1957 R: 1 LINCOLN2,313,698

HEAT EXCHANGER Filed June 23, 1954 2 Sheets-Sheet 2 am l 2565726.55

IN V EN TOR.

iUnited States Patent O HEAT EXCHAGER Roland L. Lincoln, Palos VerdesEstates, Calif. Application .lune 23, 1954, Serial No. 438,791

7 Claims. (Cl. 257-2) This invention pertains to new and novelimprovements in heat exchangers.

The invention more particularly relates to air preheaters, or the like,adapted to transfer heat from a hot gas to a gas at a lo-wertemperature.

Arrangements of this type are utilized for the purpose of recoveringheat from the escaping combustion gases from steam boiler furnaces ofpower plants and industrial plants to heat air which is to be used forsupporting combustion of the fuel in these furnaces.

in the past, equipment of this type has been identified as plate,tubular, `and regenerative systems. The plate and tubular systemsprovide a metal barrier between the combustion gases and the air to beheated, and depend for their operation upon heat being transmittedthrough metal. Velocities Iare low, with a resulting low heattransmission coefhcient. The units tend to be large, heavy, andexpensive. They do, however, prevent mixing of the combustion gases andthe air to be heated. These types are hard to clean because the small,long passages become clogged with solids deposited from the combustiongas. Inspection, cleaning, and replacement are dicult and expensive.Sulfuric acid often is formed and serious corrosion results. Theregenerative type involves baskets of metal which are slowly rotated,first in the gas stream to absorb heat, and then into the air stream togive up the heat to the air. These are more compact, lighter, andsomewhat less expensive. However, because of the passage of metal fromthe combustion gases to the air, serious leakage occurs. Because of thisleakage the size and power requirements of the forced and induced draftfans must be increased, thus adding to the cost of building andoperating the boiler.

The present invention teaches a heat exchanger arranged horizontally inheat transfer relation with a uid from which is to be extracted and asecond iiuid which is to be heated thereby.

lt is therefore an object of this invention to provide a heat exchangerhaving new and novel features of construction.

It is another object of this invention to provide a heat transfer unitcomprising a rotary tube having a portion in heat transfer relation withhot gases, and another portion in heat transfer relation with the air tobe heated.

It is another object of this invention to provide an eilicient heatexchanger having a high coefiicient of heat transfer.

It is a further object of this invention to provide a new and novelarrangement of a vertical seal operatively associated with the rotarytube to thereby provide a minimum of gas leakage between the hot gasesand the gas to be heated.

It is yet another object of this invention to provide a heat exchangertube having a captive heat transfer medium.

It is still another object of this invention to provide a heat exchangerwhich is rotatable and controllable to ICC obtain a proper heat transferrelation between the hot gases and the gas to be heated.

It is yet another object of this invention to provide a heat exchangerwhich extracts heat from combustion gases in such a manner as tomaintain the temperature of such gases above the dew point thereof(about 230 F.) to avoid condensation of corrosive vapors.

it is still another object of this invention to provide a heat exchangerof fiexible design so that many or few units may be combined inoperative relation.

It is another object of this invention to provide an arrangement that iseasy to install, easy to replace, and which may be maintained with aminimum of cost.

Other objects of invention will become apparent from the followingdescription, taken in connection with the accompanying drawings, inwhich:

Fig. 1 is a perspective View with of an arrangement of my invention;

Fig. 2 is a crosseection along the line 2 2 of Fig. l;

Fig. 3 is a view similar to Fig. 2, showing an alternative arrangementof the invention.

Fig. 4 is a View similar to Fig. 2, showing still another alternativearrangement of the invention;

Fig. 5 is a view taken along the line 5-5 of Fig. 1, illustratingshrouds which may be used for conducting gases past the heat exchanger;

Fig. 6 is a view similar to Fig. 5 showing an alternative arrangement ofthe heat exchanger.

Fig. 7 is a detail view of the seal between the two passageways;

Fig. 8 is a perspective View of Fig. 7; and

Fig. 9 is a sectional View along the line 9 9 of Fig. 2.

Referring to the drawings there is shown a casing 1 having passageway 2for conducting gases such as combustion gas from a furnace or the liketo a stack for discharge to the atmosphere in a manner well known in theart. Casing 1 also contains a passageway 3 for conducting air to thefirebox of the furnace for supporting combustion therein. Passageways 2`and 3 are divided by a wall 4. Operatively associated with saidpassageways and in heat transfer relationship with respect thereto, is aheat exch-anger element or rotor referred to generally as 5. In thepreferred form of the invention the rotor is hollow and comprises anenlarged evaporator portion 6 located in passageway 2 and a smallercondenser portion 7 located in passageway 3. Fins 8 are provided topromote transfer of heat from the hot gases to portion 6 of theexchanger, and from 7 to the gas to be heated in passageway 3. Member 5is provided with trunnions 9 and l@ mounted in suitable bearings 11 and12. A safety valve 13 prevents rupture of the rotor from excesstemperature or pressure.

At one end of the rotor there is provided a motor 14 of any suitabletype for driving member 5 with respect to the casing. Preferably this isan electric motor of the axial gap type; however, it is to be understoodthat other types of driving means, such as turbine, mechanical, or otherarrangements may be used if so desired.

A suitable seal may be provided at l5 and i6 to nrevent gas or air fromleaking into the bearings andthe operating mechanism for driving themember 5.

A seal is provided at 17 for preventing intermingling of the gases inpassageways 2 and This seal comprises a ring member 18 welded orotherwise suitably fastened to wall 4. Ring member 18 is provided with arim portion 19 against which material 21D of asbestos or the like isheld in sealing engagement by the pressure differential betweenpassageways 3 and 2. ln power plant practice passageway 3 is normallymaintained at a higher pres sure than passageway 2.

A pair of split cover rings 2.1 and 22 engage opposite parts brokenaway,

the seal illustrated in sides of material and hold the same in operativeshape by means of a bolt 23 adapted to draw cover rings 2l and 22,together. Spacer ring 2d limits the inward movement of these rings. Alsocontained between rings 2l and 2.2 is a carbon seal ring made up ofsegments 2d and held in sealing engagement with each other and withsurface 27 of member 5 by coil spring 28.

In the preferred form of the invention, member 5 is provided with anenlarged tubular portion 6 and a smaller tubular portion 7interconnected therewith. The tube contains a volatile fluid such aswater, Dowtherm, mercury, or the like. A predetermined amount of fluidis placed in the tube, depending upon the size of the tube, the type offluid, and conditions under which it will operate. Air is evacuated fromthe inside of the tube, and a combined seal and safety element isprovided at l?, in the nature of a pressureor temperature-responsiverelief de e. Member i3 will open under an excessive precalculatedtemperature or pressure condition.

Heat is absorbed from the hot gases in passageway 2 by tins S, andtransmitted to the tubular portion 6 for volatilizing the fluidcontained therein. Fins 3 are preferably round disks, but may be bladesnormal to the rotor or at other angles thereto if so desired, or othersuitable projections for increasing the effective area of the heattransfer surface. The volatilized fluid will then travel into portion 7where it will give up heat to the gas traveling in passageway 3 by wayof fins 3. Upon having heat extracted therefrom by the gas movingthrough pas sageway 3, the fluid condenses and is returned to portion 6of the tube.

Rotation of member S about its longitudinal axis will tend to throw thelluid in c? to the perimeter thereof to place the same in the bestpossible position for ready volatilization. rfhe volume of fluid is sochosen that it will cover only the inside surface of portion 6 when themember 5 is rotated. T he high velocity of the disks spinning in the hotgases transfers large quantities of heat to the metal of the disks orfins S and then through the disks and tube metal to the liquid insidethe tube. The liquid will readily boil to a vapor and in the vacuum itwill flow to the cooler portion 7 of the tube. The vapor condenses onthe inside of portion 7 and 'the released heat is corr ducted throughthe metal to the surface of disks d connected thereto where the heat istransferred to the gas passing through passageway 3. The condensedliquid llows from the smaller portion 7 of the rotor to the largerportion o, where the cycle is repeated.

Condensate resulting from the cooling of the fluid in portion 7 willreturn to portion d. Since portion 6 is larger in diameter than portion7, fluid in portion 6 will remain therein volatilized, and condensate in7 adjacent 6 will tend to how to 6. To promote the 'flow of condensatefrom 7 to 6, spiral deilectors or the like may be placed internally of'i'. Condensate will collect against these dellectors and because oftheir spiral construction, rotation of the rotor will positively movethe condensate to portion 6. The space in 7 between the deflectors thenprovides a surface relatively free of liquid for condensing fluidreceived from e.

Efciency in heat transfer is promoted by rotation of member 5. Since thevelocity difference between a gas and a member in heat transferrelationship therewith affects the elciency of heat transfer, rotationof member 5 can result in a higher heat transfer rate regardless of thevelocity of the gases in passageways Z or 3. By controlling the speed ofrotation, the gas temperature in passageway 2 may also be maintained ata temperature above the dew point at which moisture condenses out of thegas (approximately 2360" E). This is an important factor of myinvention, since condensation results in acids being deposited on themetals, with resultant corrosion.

Member 5 may be made of non-corrosive material such as stainless steelor the like, insofar as portion 6 and dus 8 connected thereto areconcerned, whereas portion 7 and the ns S connected thereto may be madeof less-expensive material. The interior of the portion 6 may be maderough to promote volatilization, whereas the condensing surfaces of '7are made smooth to permit efcient condensation.

Special wetting agents or non-rusting agents may be added if desired.

As a variation of the above two-diameter rotor of Fig. 2, the rotor maybe made in the form of a frustum of a cone, as in Fig. 3, referred togenerally as 5b, in which member 29 has attached thereto fins 8b in amanner similar to that illustrated in Fig. 2. Seal 17h is attached towall 4b and functions in the same manner and is made of the sameconstruction as seal l?. Volatile fluid 3027 is received within the`conical sector which is evacuated and provided with a safety means 13b,in the same manner as the arrangement illustrated in Fig. 2.

Still another variation of the rotor design is illustrated in Fi". 4, inwhich there is provided a solid cylindrical member 3l. provided with asleeve 32 of copper or other material having good heat transferproperties. Fins 8c are attached to member 32 and function in the samemanner as tins 8 in Fig. 2. A barrier wall le and seal 17C separate thegases in the passageways as in Fig. 2. In this form of the invention thevolatile lluid is omitted and heat is transferred through sleeve 32 andtins 8s.

Referring to Fig. 5 there is provided if so desired, regardless of theform of the rotor, shells or cases 335, 3d, 35, 36, 37, and 3S,operatively associated with a series of rotors 5. These casings followthe contour of the rotors and are spaced therefrom a predeterminedamount so as to direct the hot gases in elllcient heat transferrelationship to the portions of the rotor in its various forms.

The rotors may alternatively be arranged in staggered relationship, asillustrated in Fig. 6, with the hot gases flowing therebetween on theone end of the heat exchanger, and the gas to be heated ilowingtherebetween at the other end.

A control system may be used comprising a thermostat 42 arranged inpassageway 2 and operatively connected to motor 14 through a suitablecontrol i3 to drive the same in such a manner that the heat transferthrough the heat exchanger will be at such a value at all times that thetemperature of the hot gases through passageway 2 do not drop below apredetermined temperature (usually the dew point of the gas), thuseliminating the deposit of acid-laden condensate. Control 43 is of wellknown construction and causes motor f4 to operate between predeterminedtemperature ranges in a manner well known in the art. Arrangements ofthis type may be found illlustrated in publications as The StandardHandbook of Electrical Engineers, seventh edition, by Knowlton, section7-298; The Westinghouse Engineer, July 1956 issue, published by theWestinghouse Electric Co.; and a handbook of the American Society ofHeating and Air Conditioning Engineering, nc., 1956 Guide, chapter 39.

When it is desired to replace the heat exchangers, or clean or repairthem, it is necessary only to remove the casing 39 which is suitablybolted to casing il at d4, remove end thrust bearing 4G from shaft liti,and withdraw the rotor, together with seal i7, from the casing throughthe opening left by member 39. A new or reconditioned rotor may then beinstalled quickly and easily with a minimum of shut-down time.

Several banks of inlet and outlet passageways may be combined into thesystem if so desired, and dampers 45 may be placed in the passagewaysfor controlling passage of gases therethrough, or for closing olfcertain banks if desired for shut-down or repair purposes.

My arrangement has many advantages over present units in that a highcoeflicient of heat transfer is obtained and maintained due to the novelfeatures of construction. Not only is a high operating coefcientobtainable, but it i's maintained because of control of velocitydilferential between the rotor surface and the gas, the excellentdistribution of ow, and the fact that dirt will not be deposited, orwill tend to be removed from the heat exchanger on account of itsrotating action, and the heat transfer rate is maintained high becauseof clean surfaces.

Corrosion is reduced to a minimum because deposits of condensedacid-containing material are prevented. By maintaining the temperatureof the gas leaving the unit sufficiently high, deposits of acid areeliminated. Controlling the speed of rotation of the heat exchangerunits to control the transfer of heat prevents extracting heat from thegases to the extent of causing condensation and undesired deposits ofacid.

Additionally, gas leakage between the air passageway and the hot gaspassageway is kept at a minimum due to the novel construction of theheat exchanger and the seal used therewith.

My heat exchanger rotor is readily replaceable and, when removed, iseasy to clean and repair if necessary. Cleaning may be made in place byisolating a given bank of heat exchangers and giving them a water bathin place, using a built-in drain to collect the water.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only, and is not to be taken by way of limitation, the spiritand scope of this invention being limited only by the terms of theappended claims.

I claim:

1. In a device of the class described, walls defining a pair of adjacentpassageways, one of said passageways adapted to conduct a hot gas andthe other of said passageways adapted to conduct a cool gas, means fortransferring heat from said hot gas to said cool gas comprisinghermetically sealed heat exchanger tubes supported within said wallswith their longitudinal axes located generally horizontally, said tubesbeing each individually rotatable and comprising an evaporator portionlocated within the hot gas passageway and a condenser portion locatedWithin the cool gas passageway, a volatile fluid within said tubes,means for individually rotating each of said tubes about its respectivelongitudinal axis to throw said fluid against the periphery of saidevaporator portion to be volatilized by heat from said hot gas andthereupon ow to said condenser portion to transfer heat to said cool gasand then return to said evaporator portion, and means responsive to thetemperature of the gas in said hot gas passageway for controlling theindividual speed of rotation of said exchangers to control the rate ofheat exchange and thereby avoid reducing the temperature of said hot gasto below a predetermined Value.

2. A device as recited in claim 1 in which said evaporator portion is ofgreater diameter than said condenser portion.

3. A device as recited in claim 1 in which each said tube is in the formof a frustrum of a cone with the larger portion of the cone comprisingthe evaporator portion.

4. A device as recited in claim 1 in which each said tube is providedwith circular fins having their axes coincident with the axis of saidtube.

5. A device as recited in claim l and further including shroud means forconducting said hot gas and said cool gas in heat transfer relation withsaid plurality of heat exchanger tubes.

6. In a device of the class described, the combination of Walls defininga pair of adjacent parallel passageways of which one passageway conductsa linear stream of hot gas from which heat is to be removed and theother conducts a linear stream of cool gas to which heat is to be added,means for transferring heat from the hot gas to the cool gas comprisingan elongated, tubular, hermetically sealed element of circular outlinein transverse cross section and disposed with its longitudinal axissubstantially horizontal, said element comprising an evaporator sectionlocated within the hot gas stream and a condenser portion within thecool gas stream, said evaporator section having a cross section greaterthan said condenser portion, a body of volatile liquid contained withinthe tubular element and occupying a minor fraction of the internal spacewithin the element, a plurality of disc-like ns on and projectingradially outwardly from the element into each passageway and disposedsubstantially parallel to the direction of gas flow in each passageway,means to rotate the element and the attached ns about the horizontalaxis of the element at a rotational speed suicient to distribute theliquid in a relatively thin ilm over the interior surface of theevaporator section and means within said condenser portion for returningcondensate from said condenser portion to said evaporator section.

7. A device as recited in claim 6 and further including means responsiveto the temperature of the gas in said hot gas passageway for controllingthe speed of rotation of said element to thereby obtain optimum heattransfer at temperatures of said hot gas above a preselectedtemperature.

References Cited in the le of this patent UNITED STATES PATENTS 423,458Stollwerck Mar. 18, 1890 1,559,883 Karr et al Nov. 3, 1925 1,741,726Murray Dec. 31, 1929 FOREIGN PATENTS 108,740 Austria Sept. 15, 1927665,299 Great Britain Jan. 23, 1952

